(i) Field of the Invention
This invention relates to cosmetics and more particularly, to film-forming cosmetics, particularly film packs, which comprise copolymers of vinyl alcohol and alkyl vinyl ethers (hereinafter referred to simply as PVA/AVE).
(ii) Description of the Prior Art
Film-forming agents used in film packs (hereinafter referred to simply as pack(s)) are predominantly made of water-soluble polyvinyl alcohol polymers. The polyvinyl alcohol polymers are obtained by polymerizing vinyl acetate and saponifying the resulting polyvinyl acetate. Depending on the degree of saponification, the polymers can be classified into polymers in which all acetic groups are converted into hydroxyl group (completely saponified product: hereinafter referred to simply as PVA) and polymers in which most acetic groups are converted into hydroxyl groups while leaving part of the acetic groups (partially saponified product: hereinafter referred to simply as PVA/PVAc). In general, packs make used of polyvinyl alcohol resins having 10 to 20% of residual acetic groups in order to prevent gelation of the aqueous solution and impart flexibility to the film.
However, such PVA/PVAc is not stable because of the presence of non-saponified acetic groups. For instance, the acetic groups undergo hydrolysis as time passes, with attendant disadvantages that the pH of the pack lowers and the pack emits the odor of acetic acid. When the PVA/PVAc is added to packs in high concentration, the pack becomes so viscous that when applied to skin, the pack does not spread smoothly and is not suitable for application. In general, the PVA/PVAc has to be used in low concentration, with the results that drying of long time becomes necessary. PVA which is the completely saponified product is free of any objectionable odor and stable in pH, but because the aqueous solution becomes gelled, PVA is unsuitable as a film-forming agent for packs.